Handel, a former Georgia secretary of state, is the top Republican in many of the polls despite spending no campaign cash yet on TV advertising. But Club for Growth’s attack ad could force her to counter quickly in the crowded 18-candidate contest. Handel's campaign didn't immediately comment.

With analysts conceding a spot in the likely June 20 runoff to Democrat Jon Ossoff, Republicans are escalating their fight for the other spot. Former state Sens. Judson Hill and Dan Moody are also ratcheting up their campaigns.